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Warning

From the KPixmapCache apidocs:
KPixmapCache is susceptible to various non-trivial locking bugs and inefficiencies, and is supported for backward compatibility only (since it exposes a QDataStream API for subclasses). Users should port to KImageCache for a very close work-alike, or KSharedDataCache if they need more control

Contents

Introduction

KPixmapCache provides disk-caching of QPixmaps. If you're using SVGs or generating pixmaps from some data, you might consider using it as it eliminates the need to generate the same pixmaps over and over again.

Using it

Creating the cache object

Its API is similar to that of the QPixmapCache.
To use it, you first need to create the cache object, using a unique name:

KPixmapCache*cache=newKPixmapCache("myapp-images");

Inserting and finding pixmaps

Once that is done you can easily retrieve and insert images with insert() and find() methods:

QPixmappix("file1.png");cache->insert("file1.png",pix);QPixmappix2;if(cache->find("file2.png",pix2)){// The pixmap was loaded from cache.}else{// Pixmap was not found in the cache.// Load and insert it:pix2=QPixmap("file2.png");cache->insert("file2.png",pix2);}

The Easy Way

As loading pixmaps from files with the aid of cache is a very common operation, KPixmapCache provides a convenience method for that:

Timestamps

Often you need to make sure the cache is up-to-date and you're not using obsolete pixmaps. For this, the cache provides timestamp() method. By default it returns time when the cache was created, but you can set your own timestamp with setTimestamp() method.

// Our dataMyDataObjectdata;// Make sure the cache is up to dateif(cache->timestamp()<data.timestamp()){// Data is newer than the cache// Thus the cache is obsolete, delete and reinitialize itcache->discard();}// Here the cache is always recent enoughQPixmapvisualizedData;QStringkey("data-visualization");// Try to find the visualization from the cacheif(!cache->find(key,visualizedData)){// Visualization is not in the cache, recreate it...visualizedData=createVisualization(data);// ...and put the resulting image into cachecache->insert(key,visualizedData);}// Show the visualizedData pixmap to user

This example creates a visual representation of some data. If the data is more recent than the cache, then contents of the cache are deleted using the discard() method. Next, we check if cache already contains the necessary pixmap. If it does, then there is no need to recreate it from the data (which might be expensive).